With the increase in vehicles participating in public road traffic the demands on active and passive safety systems in vehicles have become greater as well. As a result, not only has the number of safety systems used in vehicles continued to increase over the past few years, but also their complexity. In addition to safety systems, more and more comfort systems, such as automatic level-controllers, adjustable chassis etc. are integrated in the vehicle if requested by the driver. These safety and comfort systems rely on data from a multitude of different sensors. Among the aforementioned safety and comfort systems are also so-called intelligent tires in which different variables are derived via the tire contact patch (tire contact area). For example, the condition of the road, the load state or the tire tread depth are able to be derived from the change in the tire contact patch.
Methods and devices, with whose aid it is possible to detect changes in the tire tread on the basis of an acceleration signal, the tire pressure and the temperature, are known from the related art.
From WO 02/092364, for example, a method is discussed by which the load state of a vehicle can be determined via the ratio of tire contact patch and tire circumference.
These methods all have in common that the characteristic accelerations or their peaks, which are output by a sensor installed inside the tire, are evaluated in order to measure geometric changes in the length of the tire contact patch or the tire tread. Typically, the radial acceleration signal, which is characterized by the centripetal acceleration in the round region of the tire, is analyzed, and executes a rotary motion and transitions into a translatory motion in the region of the tire contact area.
However, these methods have the disadvantage that the time signal of radial accelerations in the tire is no simple sinus or rectangular signal, but a rectangular signal that additionally exhibits an increase in the centripetal force in the entrance and exit areas of the tire contact area, and on which partially considerable vibrations caused by the road surface, the tire tread etc., for instance, are superposed.